The present invention relates to precise control of deposition or etching of thin films on a transparent substrate and, more particularly, to electroformed nozzles and formation control.
Deposition and etching by either electrochemical or solid state means are relatively slow processes that usually are controlled by establishing the rate of change and then stopping the process at a given time. However, because the processes are slow, often requiring hours or days, the chemistry of reactants can change during the process, such that precise dimensional control (e.g., to fractions of micrometers) becomes very difficult. As a result, the scrap rate for these processes can be unacceptably high.
Certain thin film processes are conducted on transparent substrates such as glass or plastic. Electroforming is one such process that can be performed on conductive glass substrates (mandrels). One field where precise dimensional control can be particularly useful is in the field of continuous ink jet printing. High resolution ink jet printing requires the droplet-forming nozzles in an array to be all essentially the same diameter so that there are no variations in darkness of print, especially for printing graphics. In addition, the uniformity of nozzle diameter is important from printhead-to-printhead so that print darkness and quality is always predictable. Although the existing art uses a means for controlling the uniformity of nozzle diameter in an array to very tight tolerances, day to day variations in electroforming bath chemistry can affect the efficiency of metal deposition so that plating to a set time does not always produce the same thickness of plating (i.e., the diameter can vary).
It is seen then that there exists a need for a means for precise dimensional control of dimensions produced by deposition or etching processes.
In accordance with the present invention, a real time control device for electroformation of precise diameter nozzles is proposed, by microscopically measuring the orifice through a transparent substrate with video image analysis. The present invention utilizes the horizontal plating arrangement, a transparent plating mandrel, and video measurement techniques to provide real time control of electroforming to make nozzles having diameter variations of less than one micrometer.
In accordance with one aspect of the present invention a method has been developed to accurately measure the growth of a deposit during the deposition on one side of a transparent substrate. The present invention utilizes the special attributes of the plating cell arrangements for precise control of the orifice diameter as it is being formed. In particular, precise control of deposition or etching of thin films on a transparent substrate is achieved using a computer based measuring system to measure, in real time, a test feature whose measured dimensions are representative of the dimensions of the desired features of the object being processed. The rate of material deposition and removal is controlled based on the measured value of the test feature. In particular, a video camera and microscope are used to produce images of the test feature.
Other objects and advantages of the invention will be apparent from the following description and the appended claims.